1. Field of the Invention
The present invention relates to a radial oil seal having a first seal ring with a seal lip formed of rubber and a second seal ring with a seal lip formed of synthetic resin integrally assembled with each other.
2. Description of the Prior Art
There has hitherto been known a conventional type of radial oil seal which is, for example, shown in FIG. 11 (c.f. Japanese utility model registration application laid open to public inspection under Serial No. 43-1971). Specifically, in FIG. 11, reference numeral 100 designates a first seal ring having a seal lip 102 of rubber extending axially to the sealed fluid side or to the right in FIG. 11, the distal end or edge of the rubber seal lip 102 being in sealing contact with the outer peripheral surface of a rotation shaft 101 so as to form a first seal part. Reference numeral 103 designates a second seal ring having a seal lip 104 of synthetic resin extending axially toward the sealed fluid side along the back face of the rubber seal lip 102, the distal end or edge of the synthetic resin seal lip 104 being in sealing contact with the outer peripheral surface of the rotation shaft 101 so as to form a second seal part. The first and second seal rings 100, 103 are integrally assembled in this order to an outer ring 105 of metal press fitted into a housing 106 from the sealed fluid side. Here, it is to be note that although the seal lip 104 of synthetic resin is excellent in sliding property and anti-friction property, it involves the disadvantages that the sliding surface of the seal lip 104, if it is used independently or singly, is liable to be injured upon insertion thereinto of the ratation shaft 101, and it takes a relatively long time for the sliding surface of the seal lip 104 to come in intimate contact with the relatively coarse surface of the rotation shaft 101, thus resulting in an initial-period leakage of fluid to be sealed. In view of this, the seal lip 104 of synthetic resin is ordinarily used in combination with a rubber seal lip, as referred to above and shown at 102 in FIG. 11, so that effective sealing is made by means of the rubber seal lip 102 so as to prevent any possible initial-period leakage of fluid until the time when the sliding surface of the synthetic resin seal lip 104 comes in intimate sealing contact with the coarse surface of the rotation shaft 101. On the other hand, the rubber seal lip 102, when subjected to a high pressure, increases in sliding resistance thereby to accelerate sliding wear thereon as the contact pressure per unit area of the rubber seal lip 102 against the rotation shaft 101 increases, and hence the rubber seal lip 102 is not suitable for sealing of the fluid under high pressure. Such a situation can be improved by means of the seal lip 104 of synthetic resin which serves to support the back face of the rubber seal lip 102 so as to share the pressure applied by the fluid to be sealed to the rubber seal lip 102, as a consequence of which an increase in contact pressure per unit area of the rubber seal lip 102 against the rotation shaft 101 is suppressed in an effective manner, thereby permitting the rubber seal lip 102 to serve for sealing of high pressure fluid for an extended period of use.
With the conventional type of radial oil seal as described above, however, a bent portion 107 of the synthetic resin seal lip 104 is low in bending strength in the dirction in which the pressure of the fluid to be sealed is applied to the seal lip 104, so that the synthetic resin seal lip 104 is easily caused to deform under the fluid pressure applied thereto through the rubber seal lip 102 with its lip end 104a being displaced toward the air side to make the back face of the seal lip 104 in areal contact with the outer periphery of the rotation shaft 101 in place of the line contact therebetween, thus increasing the area of contact therebetween to a substantial extent. As a result, the pressure of contact per unit area of the synthetic resin seal lip 104 against the rotation shaft 101 is accordingly reduced to lower the sealing performance. In addition, the sliding surface of the synthetic resin seal lip 104 is liable to be injured by dust coming into the housing 106 from the ambient air, giving rise to a leakage of fluid to be sealed.